Current anti-lock brake systems only control the pressure of the brake fluid applied to a brake actuator for one of the rear wheels and use a copy valve which controls the pressure of the brake fluid applied to the brake actuator of the other rear wheel. The copy valve reproduces the pressure of brake fluid applied to the brake actuator of the second rear wheel so that it will be substantially the same as the pressure of the brake fluid being applied to the brake actuator being controlled by the anti-lock brake system.
Leiber, in U.S. Pat. No. 4,600,244, and De La Broise et al., in U.S. Pat. No. 4,886,321, disclose diagonally-split anti-lock brake systems using a single copy valve to control the brake pressure being applied to the brake actuator of one of the rear wheels. Wetzel, in U.S. Pat. No. 5,131,729, discloses a diagonally-split anti-lock brake system which uses two copy valves to control the brake pressure applied to each rear wheel to be the same as applied to its diagonally associated front wheel. Leiber, in U.S. Pat. No. 4,033,637, teaches a vertical anti-lock brake system using a single copy valve causing the pressure applied to the brake actuators of the rear wheels to be a copy of the pressure applied to the brake actuators of the front wheels. While Farr, in U.S. Pat. No. 4,893,881, discloses a diagonally-split anti-lock brake system using two copy valves to copy the pressure of the brake fluid applied to the controlled rear wheel brake actuator to the uncontrolled brake actuator of the other rear wheel.
The prior art teaches various types of copy valves for anti-lock brake systems. The copy valve disclosed herein is an improved copy valve for anti-lock brake systems.